Alternate-current dielectric-barrier-discharge (AC-DBD) plasma actuators, as a main mechanism, impart wall-parallel momentum to the environment by ionization of air molecules. This characteristic turned out to be advantageous in flow-control, addressing skin-friction drag reduction, hence a decrease in emissions for aerodynamic vehicles.
In turbulent flows both streamwise travelling waves of spanwise wall velocity (Quadrio et al., 2009, JFM) and spanwise wall oscillations (Quadrio & Ricco, 2004, JFM) have demonstrated to be capable of reducing drag by up to 40 %. The spanwise oscillating wall relies on a periodic fluid motion transverse to the mean-flow direction, generating a so-called Stokes-layer. In experiments, this was formerly achieved by mechanically displacing a wall, tested in the wind-tunnel facility of ISTM that is dedicated for accurate skin-friction measurements in airflow (Gatti et al., 2015, Exp. Fluids). In the current research project a plasma actuator concept was evaluated that is capable of exciting flow oscillation in the spanwise direction (see figure 1).
Figure 1: (Left) Plasma actuator array in operation and (right) velocity fields in a cross-plane for two opposing phase angles of the oscillation.
Within this framework investigations on body-force determination under influence of an external airflow are to be performed in another blower-type wind tunnel in order to estimate the performance changes of a plasma actuator when operated as flow-control device. This is very important for both modelling plasma actuators in numerical simulations and anticipating their flow-control ability for different free-stream velocities.
The elaborated actuator concept for spanwise oscillation will be further tested to analyse the flow manipulation in non-quiescent conditions. As a final milestone, it is planned to implement the plasma actuator in a turbulent flow and measure the impact on skin friction in the available facility.